1. Field of the Invention
This invention relates to an adjusting device of a chair backrest, particularly to one able to smoothly adjust the height of the backrest and keep it securely positioned at the adjusted height.
2. Description of the Prior Art
Commonly, most of conventional chairs have the seat and the backrest immovably made, not adjustable. Or, another one has the backrest possible to be altered with diverse inclined angles so as to meet a user's preference. However, as the backrest of a conventional chair is always positioned at a certain level, it cannot be adjusted to change its vertical position in accordance with a user's posture or height to effectively support his back.